A digital image forming apparatus equipped with an optical scanner unit which is detachable from a main body typically includes in its upper part an image reading section, and in its lower part an image holding member and an image forming section. The image reading section outputs a document image in a form of an electric image signal using a line image sensor, etc. The image forming section develops an electrostatic latent image formed on an image holding member and transfers it onto a sheet, and also performs cleaning. The optical scanner unit is provided for forming an electrostatic latent image on a surface of a photoreceptor by scanning an optical image by projecting thereon a laser beam. The described optical scanner unit is provided between the image reading section and the image forming section in consideration of a space, image forming processes, etc.
The optical scanner unit and the image forming section including the image holding member, etc., are respectively composed of many members which are often subject to cleaning and exchange, etc., and for the described purposes, the optical scanner unit and the image forming section are often removed from the digital image forming apparatus.